A. Field of the Invention
The present invention relates to a new and improved valve assembly for controlling the flow of fluid from first and second fluid sources to one or more motors in order to provide increased motor speeds when demanded, and to a new and improved method for providing greater motor speeds in a hydraulic system.
B. Description of the Prior Art
Typically, in vehicles of the type powered by a hydraulic motor, such as a grass mower for golf greens, there are provided neutral, reverse and forward modes. The forward or working mode of the motor is a slow speed employed while the vehicle is used to mow a golf green. The motor speed in this mode must be slow in order to avoid uneven grass cutting.
Once the vehicle has completed a job; for example, once a green is mowed, it is necessary to move to another job or green or return to the storage area. During this mode of operation, the transportation mode, a faster drive speed is desired.
To obtain the various modes of operation and the transportation mode of operation, prior art valve assemblies include a spool valve having one or more lands for communicating pressurized fluid to the motors in a first direction for reverse operation of the motors and in a second direction for forward operation. In a third or neutral mode the prior art spool valves direct the fluid to a reservior. For the fourth or transportation mode of the motors the prior art valve assemblies have a fourth position for the single spool valve whereby pressurized fluid is directed to the motors at the appropriate times. This fourth valve position may either increase the amount of flow from a single fluid source to the motor or introduce fluid from a second source and combine the flows from both sources to the motor, thus increasing the motor speed.
These prior art devices employ complex coring arrangements, have poor metering characteristics and high leakage rates due to small sealing lands necessary on the single valve. In addition, these valves are normally manually operated into the fourth position resulting in abrupt introduction of the increased fluid flow with resultant detrimental pressure spikes.